In recent years, it has become commonplace to use optical recording media as recording media, and a plurality of types of optical recording media of different recording capacities and standards are widely prevalent. For optical recording media of different standards, light sources of different wavelengths are used for recording or reproduction. Therefore, an optical disk apparatus which supports a plurality of types of optical recording media includes a plurality of light sources to be used for recording or reproduction.
FIG. 27 schematically shows the configuration of an optical system in an optical head of a conventional optical disk apparatus. This optical disk apparatus is disclosed in, for example, Japanese Laid-Open Patent Publication No. 2001-184698. The optical disk apparatus shown in FIG. 27 has a light source device 1603, which includes a light source 1601 for emitting light of a wavelength λ1 and a light source 1602 for emitting light of a wavelength λ2 (λ1<λ2) that are placed in a single package.
When performing recording or reproduction for a first optical recording medium 1609, the light source 1601 is used. Light 1604 which is emitted from the light source 1601 is led through a collimating lens 1605, reflected by a mirror 1606, and converged by a converging lens 1608 onto the first optical recording medium 1609. Light which is reflected from the first optical recording medium 1609 follows an opposite optical path to reach the mirror 1606, and a portion thereof is transmitted through the mirror 1606. Further passing through a detection lens 1610, the light enters a photodetector 1611. The light entering the photodetector 1611 is detected by a photosensitive device within the photodetector 1611, whereby control signals for focus control and tracking control and a reproduction signal containing information which has been recorded on the first optical recording medium 1609 are generated.
When performing recording or reproduction for a second optical recording medium 1613, the light source 1602 is used. Light 1612 emitted from the light source 1602 is led through the collimating lens 1605, reflected by the mirror 1606, and converged by the converging lens 1608 onto the second optical recording medium 1613, which has a different substrate thickness from that of the first optical recording medium 1609. Light which is reflected from the information optical recording medium 1613 follows an opposite optical path to reach the mirror 1606, and a portion thereof is transmitted through the mirror 1606. Further passing through the detection lens 1610, the light enters the photodetector 1611. As in the case of the first optical recording medium 1609, the light entering the photodetector 1611 is detected by the photosensitive device within the photodetector 1611, whereby control signals for focus control and tracking control and a reproduction signal containing information which has been recorded on the first optical recording medium 1609 are generated.
As described above, in the optical disk apparatus of FIG. 27, the light source 1601 and the light source 1602 are accommodated in a single package. This is so that, by disposing the light sources of different wavelengths in substantially the same place, rays of light emitted from the two light sources share the same optical path, thus simplifying the structure of the optical system. As a result, the outer figure of the entire optical head including the optical system can be reduced, and the costs associated with the optical head can be reduced.
However, the light source 1601 and the light source 1602 disposed in the light source device 1603 cannot be positioned in exactly the same place. Therefore, as schematically shown in FIG. 27, the optical axis of the light 1604 emitted from the light source 1601 and the optical axis of the light 1612 emitted from the light source 1602 do not coincide with each other. For example, if the optical axis of the light 1604 emitted from the light source 1601 is made to coincide with the optical axis of the converging lens 1608, then the optical axis of the light 1612 emitted from the light source 1602 will not coincide with the optical axis of the converging lens 1608, but will be shifted therefrom.
As a result, when performing recording or reproduction for the second optical recording medium 1613 by using the light source 1602, aberration (chiefly coma) occurs in the beam spot which is converged on the second optical recording medium 1613. Thus, there occurs a problem in that recording or reproduction of information cannot be properly performed, and the recording or reproduction performance deteriorates.
In particular, when performing recording for an optical recording medium, there may occur a problem in that recording marks of an appropriate shape cannot be formed on the tracks because of aberration occurring in the beam spot which is converged on the optical recording medium.
As optical recording media increase in recording density, the recording marks will have smaller shapes, and the track intervals will become narrower. Therefore, in the case of optical recording media of high recording density, such problems may become even more serious.